Laboratory studies of the interaction of carbon monoxide with water ice     

M.P. Collings  J.W. Dever  H.J. Fraser  M.R.S. McCoustra 《Astrophysics and Space Science》2003,285(3-4):633-659

The interaction of carbon monoxide (CO) with vapour-deposited water(H₂O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption from amorphous H₂Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as the water ice crystallises and then desorbs. The astronomical implications of this model are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Effects of variable winds on biological productivity on continental shelves in coastal upwelling systems     

Louis W. Botsford  Cathryn A. Lawrence  Edward P. Dever  Alan Hastings  John Largier   《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):3116

The production and distribution of biological material in wind-driven coastal upwelling systems are of global importance, yet they remain poorly understood. Production is frequently presumed to be proportional to upwelling rate, yet high winds can lead to advective losses from continental shelves, where many species at higher trophic levels reside. An idealized mixed-layer conveyor (MLC) model of biological production from constant upwelling winds demonstrated previously that the amount of new production available to shelf species increased with upwelling at low winds, but declined at high winds [Botsford, L.W., Lawrence, C.A., Dever, E.P., Hastings, A., Largier, J., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259]. Here we analyze the response of this model to time-varying winds for parameter values and observed winds from the Wind Events and Shelf Transport (WEST) study region. We compare this response to the conventional view that the results of upwelling are proportional to upwelled volume. Most new production per volume upwelled available to shelf species occurs following rapid increases in shelf transit time due to decreases in wind (i.e. relaxations). However, on synoptic, event time-scales shelf production is positively correlated with upwelling rate. This is primarily due to the effect of synchronous periods of low values in these time series, paradoxically due to wind relaxations. On inter-annual time-scales, computing model production from wind forcing from 20 previous years shows that these synchronous periods of low values have little effect on correlations between upwelling and production. Comparison of model production from 20 years of wind data over a range of shelf widths shows that upwelling rate will predict biological production well only in locations where cross-shelf transit times are greater than the time required for phytoplankton or zooplankton production. For stronger mean winds (narrower shelves), annual production falls below the peak of constant wind prediction [Botsford et al., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259], then as winds increase further (shelves become narrower) production does not decline as steeply as the constant wind prediction.  相似文献   

Evaporation of ices near massive stars: models based on laboratory temperature programmed desorption data     

Serena Viti  Mark P. Collings  John W. Dever  Martin R. S. McCoustra  David A. Williams 《Monthly notices of the Royal Astronomical Society》2004,354(4):1141-1145

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The evolution and depth structure of shelf and slope temperatures and velocities during the 1997–1998 El Niño near Point Conception, California     

E. P. Dever  C. D. Winant 《Progress in Oceanography》2002,54(1-4)

Moored, survey, and drifter observations are used to describe the evolution of temperature, sea level, velocity and salinity from 1997 to 1998 over the California shelf, between San Luis Obispo Bay and the eastern entrance to the Santa Barbara Channel. The dominant event during this time was the 1997–1998 El Niño. Its relation to background seasonal and interannual variability depended on which property is considered. Subsurface temperature and local sea level showed extreme anomalies between March 1997 and October 1998. Three distinct peaks occurred. The first two are associated with the regional response to El Niño, while the cause of the third remains unclear. The first peaked in June 1997, and decayed until August. The main El Niño peak reached maximum amplitude between November 1997 and January 1998. After the collapse of the regional El Niño anomaly in February 1998, a final peak occurred locally during the summer of 1998.The central result presented here concerns the spatial structure of temperature during these events. The initial peak was surface intensified and was barely detectable at 45 m. Its amplitude varied with position along the coast, decaying with distance north. The main peak showed a strong signal down to at least 200 m. The amplitude and timing of temperature anomalies during this event were depth dependent. The largest absolute amplitudes relative to seasonal cycles were in excess of 4 °C and occurred between 45 and 65 m depth. The anomalies reached their maximum values at later time with increasing depth, between October 1997 and January 1998. The amplitude of this main peak was comparable at all mooring sites. The final peak in August 1998 had a comparable amplitude at all mooring sites to a depth of 100 m. Temperature increases during the three events were accompanied by a corresponding rise in sea level.The El Niño signals in currents and salinity are more difficult to distinguish from background variability than those in temperatures and sea level. However, stronger than average poleward flow was observed at the eastern entrance to the Santa Barbara Channel between 5 and 100 m depth for most of 1997, and there are indications for greater than usual poleward flow over the Santa Maria Basin in fall 1997. Surface drifter evidence, although qualitative, also suggests greater than usual poleward displacement in November 1997 relative to other years. Along with increased temperature, survey observations of salinity suggest changes to the regional temperature–salinity relation during November 1997 with greater than usual salinity at temperatures below 12 °C.  相似文献   

WEST: A northern California study of the role of wind-driven transport in the productivity of coastal plankton communities   总被引：1，自引：0，他引：1  

J.L. Largier  C.A. Lawrence  M. Roughan  D.M. Kaplan  E.P. Dever  C.E. Dorman  R.M. Kudela  S.M. Bollens  F.P. Wilkerson  R.C. Dugdale  L.W. Botsford  N. Garfield  B. Kuebel Cervantes  D. Kora in 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):2833

The “Wind Events and Shelf Transport” (WEST) program was an interdisciplinary study of coastal upwelling off northern California in 2000–03. WEST was comprised of modeling and field observations. The primary goal of WEST was to better describe and understand the competing influences of wind forcing on planktonic productivity in coastal waters. While increased upwelling-favorable winds lead to increased nutrient supply, they also result in reduced light exposure due to deeper surface mixed layers and increased advective loss of plankton from coastal waters. The key to understanding high levels of productivity, amidst these competing responses to wind forcing, is the temporal and spatial structure of upwelling. Temporal fluctuations and spatial patterns allow strong upwelling that favors nutrient delivery to be juxtaposed with less energetic conditions that favor stratification and plankton blooms. Observations of winds, ocean circulation, nutrients, phytoplankton and zooplankton off Bodega Bay and Point Reyes (38°N) were combined with model studies of winds, circulation and productivity. This overview of the WEST program provides an introduction to the WEST special issue of Deep-Sea Research, including the motivation for WEST, a summary of study components, an integrative synthesis of major research results to-date, and background on conditions during field studies in May–June 2001 (the upwelling period on which this special issue is focused).  相似文献   

Apport des isotopes stables dans l'estimation des altitudes de recharge de sources thermales du MarocRecharge altitude estimation of thermal springs using stable isotopes in Morocco     

Anne Winckel  Christelle Marlin  Laurent Dever  Jean-Luc Morel  Karim Morabiti  Mohamed Ben Makhlouf  Ahmed Chalouan 《Comptes Rendus Geoscience》2002,334(7):469-474

The recharge altitude estimation of thermal springs from northern and eastern Morocco using ¹⁸O and ²H contents requires the definition of regional isotopic altitudinal gradients (?0.25‰ for 100 m for the Rif and ?0.30‰ for the East) and the calculation of residence time using ¹⁴C. The altitudes of emergence vary widely between 170 and 1040 m under the altitude of the recharge areas. The ¹⁸O and ²H compositions of palaeowaters ($\text{>10}\text{000}$ yr BP) indicate two effects, altitude and palaeoclimate. To cite this article: A. Winckel et al., C. R. Geoscience 334 (2002) 469–474.  相似文献   

Video monitoring of in-channel wood: From flux characterization and prediction to recommendations to equip stations     

Zhi Zhang  Hossein Ghaffarian  Bruce MacVicar  Lise Vaudor  Aurélie Antonio  Kristell Michel  Hervé Piégay 《地球表面变化过程与地形》2021,46(4):822-836

Wood flux (piece number per time interval) is a key parameter for understanding wood budgeting, determining the controlling factors, and managing flood risk in a river basin. Quantitative wood flux data is critically needed to improve the understanding of wood dynamics and estimate wood discharge in rivers. In this study, the streamside videography technique was applied to detect wood passage and measure instantaneous rates of wood transport. The goal was to better understand how wood flux responds to flood and wind events and then predict wood flux. In total, one exceptional wind and seven flood events were monitored on the Ain River, France, and around 24,000 wood pieces were detected visually. It is confirmed that, in general, there is a threshold of wood motion in the river equal to 60% of bankfull discharge. However, in a flood following a windy day, no obvious threshold for wood motion was observed, which confirms that wind is important for the preparation of wood for transport between floods. In two multi-peak floods, around two-thirds of the total amount of wood was delivered on the first peak, which confirms the importance of the time between floods for predicting wood fluxes. Moreover, we found an empirical relation between wood frequency and wood discharge, which is used to estimate the total wood amount produced by each of the floods. The data set is then used to develop a random forest regression model to predict wood frequency as a function of three input variables that are derived from the flow hydrograph. The model calculates the total wood volume either during day or night based on the video monitoring technique for the first time, which expands its utility for wood budgeting in a watershed. A one-to-one link is then established between the fraction of detected pieces of wood and the dimensionless parameter “passing time × frame rate ”, which provides a general guideline for the design of monitoring stations.  相似文献   

Hillslope and point based soil erosion – an evaluation of a Landscape Evolution Model     

G.R. Hancock  T. Wells  C. Dever  M. Braggins 《地球表面变化过程与地形》2019,44(5):1163-1177

Excessive soil erosion and deposition is recognised as a significant land degradation issue. Quantifying soil erosion and deposition is a non-trivial task. One of these methods has been the mathematical modelling of soil erosion and deposition patterns and the processes that drive them. Here we examine the capability of a landscape evolution model to predict both soil erosion rate and pattern of erosion and deposition. This numerical model (SIBERIA) uses a Digital Elevation Model (DEM) to represent the landscape and calculates erosion and deposition at each grid point in the DEM. To assess field soil redistribution rates (SRR) and patterns the distribution of the environmental tracer ¹³⁷Cs has been analysed. Net hill slope SRR predicted by SIBERIA (a soil loss rate of 1.7 to 4.3 t ha^-1 yr^-1) were found to be in good agreement with ¹³⁷Cs based estimates (2.1 – 3.4 t ha^-1 yr^-1) providing confidence in the predictive ability of the model at the hillslope scale. However some differences in predicted erosion/deposition patterns were noted due to historical changes in landscape form (i.e. the addition of a contour bank) and possible causes discussed, as is the finding that soil erosion rates are an order of magnitude higher than likely soil production rates. The finding that SIBERIA can approximate independently quantified erosion and deposition patterns and rates is encouraging, providing confidence in the employment of DEM based models to quantify hillslope erosion rates and demonstrating the potential to upscale for the prediction of whole catchment erosion and deposition. The findings of this study suggest that LEMs can be a reliable alternative to complex and time consuming methods such as that using environmental tracers for the determination of erosion rates. The model and approach demonstrates a new approach to assessing soil erosion that can be employed elsewhere. © 2018 John Wiley & Sons, Ltd.  相似文献   

Geochemistry and residence time estimation of groundwater from the upper aquifer of the Chihuahua desert (Comarca Lagunera, Northern Mexico)     

Laurent Brouste  Christelle Marlin  Laurent Dever 《Applied Geochemistry》1997,12(6):775-786

178 groundwater and surface waters have been sampled from April to September 1994 in an endoreic basin located in the N of Mexico (Comarca Lagunera). In this area, groundwater has been exploited over the past century mainly for irrigation and cattle supply. Recent intensive pumping has caused the lowering of the water table at a rate of 1 m a⁻¹ Chemical analyses have been performed on all collected samples and 37 of them have been selected for isotopic measurements (¹⁸O,²H,¹³C and¹⁴C). Water stable isotope contents (¹⁸O,²H) show an increasing evaporation of the groundwater towards the Nazas river. They also indicate that the recharge occurs from the Nazas river and from the mountains surrounding the depression (Sierra Madre Occidental). Water presents a large spatial variability of the chemical facies (SO₄Ca, SO₄ClNa, HCO₃-Ca and HCO₃-Na) which is in relation with (i) their interaction with the geological formations of the basin (carbonates, gypsum and various silicates) and (ii) evaporation. This evaporation occurs in the upper part of the unsaturated zone during infiltration especially for the groundwater sampled near the Nazas river. The¹⁴C activity varies between 110.4 (± 1.1) and 4.0 (±0.2) pmc. The¹³C contents of the total dissolved inorganic C (TDIC) range between −11.0 and −3.6‰. The calculated¹³C contents of the CO₂ in equilibrium with the TDIC, varying between −18.4%0 to −10.9% indicate two origins of C in solution: the carbonate matrix (δ¹³C= +0.9‰) and the soil CO₂ (δ¹³C from −27.7‰ to −21.7‰ for the cultivated areas). Mean residence times have been determined after correction of the initial activities for dead C from the rock matrix. The mean residence times confirm a modern recharge of the groundwater from the Nazas and indicate the presence of palaeowaters in the northern and southern parts of the basin (up to 30 ka BP).  相似文献   

A Test of Bycatch Reduction Devices on Commercial Crab Pots in a Tidal Marsh Creek in Virginia     

A. Scott Morris  Stephanie M. Wilson  Erik F. Dever  Randolph M. Chambers 《Estuaries and Coasts》2011,34(2):386-390

The effectiveness of bycatch reduction devices (BRDs) on commercial pots designed to capture blue crabs Callinectes sapidus was tested in the York River on Felgates Creek (37.2667 N, −76.5850 W) over the period 4 June through 31 July 2009. For each of 10 pairs of pots, one had BRDs affixed to all four entrance gapes and the other had none. Pots were baited approximately once each week but were sampled for blue crabs and bycatch 6 of 7 days each week for the duration of the study. More than one fourth of 1,643 total crabs were caught on the first day after baiting, and for these 7 days, no statistical difference was detected between either the number or size of legal-size crabs caught in BRD versus non-BRD pots. Of 51 Malaclemys terrapin and 44 fish caught as bycatch throughout the study, all but three fish were captured in non-BRD pots. BRDs exclude bycatch and may reduce incidental mortality of crabs in pots that are not tended regularly.  相似文献